diff --git a/test/rails_development_boost_test.rb b/test/rails_development_boost_test.rb
index 781f664..1dd974b 100644
--- a/test/rails_development_boost_test.rb
+++ b/test/rails_development_boost_test.rb
@@ -125,7 +125,7 @@ def assert_different_object_id(*expressions, &block)
   end
   
   def each_object_id_diff(alter, expressions)
-    ids_before = expressions.map { |expr| [expr.dup, eval("#{expr.dup}.object_id")].dup }
+    ids_before = expressions.map { |expr| [expr, eval("#{expr}.object_id")] }
     alter.call
     ids_before.each do |expr, before|
       after = eval("#{expr}.object_id")